This invention relates to collectors for electron beam tubes.
Linear electron beam tubes are used for the amplification of rf signals. They incorporate an electron gun for the generation of an electron beam of the appropriate power. The electron gun has a cathode heated to a high temperature so that the application of an electric field results in the emission of electrons, the electric field being produced by spacing an anode in front of and some distance from the cathode. Typically, the anode is held at around potential and the cathode at a large, for example, several tens of kilovolts, negative potential.
In one type of linear beam tube called an Inductive Output Tube (IOT), a grid is placed close to and in front of the cathode and an rf signal to be amplified is applied between the cathode and grid so that the electron beam generated in the gun region is density modulated. The density modulated electron beam is directed through an rf interaction region which includes one or more resonant cavities. The beam may be focussed by magnetic means, to ensure that it passes through the rf region, and delivers power at an output section where the amplified rf signal is extracted.
After passing through the output section the beam enters a collector where it is collected and the remaining power on it is dissipated. The amount of power needing to be dissipated depends upon the efficiency of the linear beam tube, this being the difference between the power of the beam generated at the electron gun region and the rf power extracted in the output coupling of the rf region.
A collector may consist of a single conductive component, usually of copper, which operates at ground potential or close to ground potential. It is known to improve the overall efficiency of an amplifier tube by using a collector consisting of a number of electrically isolated stages each operating at a respective potential at or between ground and cathode potential. In one such typical arrangement for a high power klystron used for the amplification of television signals at uhf frequencies the collector has 5 stages, the difference in potential between the various stages being 25% of the beam voltage. By using such a multi-stage collector, the electrons in the beam are slowed down before impacting on the electrode surfaces thus leading to greater recovery of energy. Collectors may of course have a different number of stages operating at different potentials to effect an energy saving.